Gov. Jerry Brown hopped around Europe for two weeks last month, telling the world that to avoid a climate change Armageddon, it should emulate what California is doing to reduce greenhouse gas emissions.

As Brown was crusading in Europe, his Air Resources Board issued a report hailing California’s nearly 5 percent reduction in emissions of carbon dioxide and other gases in 2016 by companies governed by the state’s “cap-and-trade” system.

It appeared to underscore the efficacy of the system, whose extension was one of Brown’s proudest achievements this year and one he forcefully touted in Europe.

Appearances, however, can be deceiving.

Julie Cart, the environmental writer for CALmatters who covered Brown’s European sojourn, delved into the report’s data and discovered that the major reason for last year’s drop in emissions wasn’t cap-and-trade, or any other state action.

Rather, it occurred because unusually heavy winter rain and snow storms allowed utilities to depend less on generating electricity by burning fossil fuels and more on hydroelectric power from dams in California and other states.

California utilities are under a legal mandate to shift their power supplies from coal, natural gas and other carbon-emitting sources to carbon-free “renewable portfolios” — 33 percent by 2020 and 50 percent by 2030.

The latter requirement is imposed by 2015 legislation carried by Senate President Pro Tem Kevin de León, who was part of Brown’s climatic posse in Europe.

However, the state’s definition of renewable sources specifically excludes the hydroelectric power from major dams such as Shasta, Oroville and Folsom that was the major reason greenhouse gas emissions dropped so dramatically in 2016.

De León’s bill, in expanding the mandate to 50 percent, actually tightened uses of “small hydroelectric generation” to meet it.

Why the official shunning of non-polluting hydroelectric generation?

Simply put, environmental activists just don’t like big dams for reasons that have nothing to do with climate change — even though we will need more water storage to capture winter rains if, as they contend, climate change reduces winter snowfall.

And then there’s nuclear power. It’s noteworthy that France has achieved the globe’s most dramatic reduction in greenhouse gases by shifting 80 percent of its power supply to nuclear, and that China is building more nuclear facilities as it tries to wean itself from coal.

However, one big atomic plant in Southern California, San Onofre, has been closed and the remaining one near San Luis Obispo, Diablo Canyon, is also ticketed for closure.

Finally, Brown’s pet bullet train project receives a quarter of all cap-and-trade auction revenues on the assertion that its electrified service will reduce greenhouse gas emissions. However, the Legislature’s budget analyst has concluded that construction will actually add more emissions in the short run. Meanwhile, the High-Speed Rail Authority’s own projection is that even when fully built, it would reduce automotive traffic — the largest single source of those emissions — by scarcely 1 percent.

It’s not quite as simple as Brown would have us — and the rest of the world — believe.

Dan Walters has been a journalist for nearly 57 years, many as a columnist with the Sacramento Bee. CALmatters is a nonprofit journalism venture focused on engaging Californians in how their state government works and why it matters.